I was able to reproduce your error, and it was a memory problem. I have resolved that problem, but hit a new limit of approx 15k x 10k, which is a limit imposed by the Windows bitmap maximum size. This change will be in the next release of the plugin.

Can you also adjust the limit of the slider as well as this is very confusing.

There is now a popup msg if there is insufficient RAM to paint the rendered image onto the Viewport.

If this is a Windows bitmap memory issue then why does Octane allow people to render 65K x 65K on the slider?

The Rhino plugin has C# component that runs as a Rhino plugin, and a C++ component that interfaces with Octane, and it's the transferral of the rendered image from the C++ component to the C# component that is failing due to the Windows API not being able to create a large enough bitmap. If you have more than 16GB RAM you may find you can render much larger resolutions - but I'm not sure.

"The Rhino plugin has C# component that runs as a Rhino plugin, and a C++ component that interfaces with Octane, and it's the transferral of the rendered image from the C++ component to the C# component that is failing due to the Windows API not being able to create a large enough bitmap. If you have more than 16GB RAM you may find you can render much larger resolutions - but I'm not sure."

I have tried the same file on a machine with 32GB of RAM and 4X GTX 1080 Ti, it still failed. Same as the one with 16GB of RAM.